package org.mikeliu.zzjexp1;

import java.util.Scanner;

public class Exp2 {
	public static void main(String[] args) {
		int n;
		Scanner scanner=new Scanner(System.in);
		n=scanner.nextInt();
		double sum = 0;
		for (int i=2; i<=2*n; i+=2) {
			sum=sum+(1.0/i);
		}
		System.out.printf("%.4f",sum);
		scanner.close();
		return;
	}
}
